provide clear indication of file state

when a big project is loaded (say, the qt5 top-level project), it can take quite some time until the c++ editor becomes fully functional. while it's possible to figure out what is going on when one knows where to look, this isn't a very good UX.

therefore, i suggest that editors gain some indicator (maybe a top-level status bar? might be a bit jumpy) that shows missing dependencies, maybe like this:

• "the editor is not fully functional, as the file's project association has not been determined yet." this is mostly redundant with the 'Scan "qt5" project tree' status of the cmake project manager, which i had to grep qtc source code for to figure out. but for files which are actually not part of any project, that would be valuable info regardless.
• "the editor is not fully functional, as the code model has not processed the file yet." (this is redundant with the code models "Parsing ..." status of the code model)
• etc.